*Featured image photo credit: Redouan Bshary

In this episode, Zegni Triki (new PI fall 2022, University of Bern, Switzerland) takes us on a wild journey under the sea to learn about cleaner fish mutualisms on the great barrier reef in her paper: Triki, Richter et al. 2022: ‘Marine Cleaning Mutualism Defies Standard Logic of Supply and Demand.’ Zegni tells tales of the complex natural history of cleaner fish and explains how models can help dissect messy, sometimes confusing empirical data. We also discuss the value of incorporating individual decision making into biological market theories of mutualistic species interactions. Plus, we learn once and for all who has the best mucus on the reef. Listen to our conversation and then read Zegni’s full paper here!

Dive even deeper by emailing your questions to Zegni at zegni.triki@gmail.com.

And learn more about the Lizard Island Research Station here: https://lirrf.org/

NATURALIST SELECTIONS IS AN INTERVIEW SERIES PRODUCED BY THE AMERICAN SOCIETY OF NATURALISTS GRADUATE COUNCIL. WE SHOWCASE GRADUATE STUDENT AND POSTDOC AUTHORED WORK IN THE AMERICAN NATURALIST, A PREMIER PEER-REVIEWED JOURNAL FOR ECOLOGY, EVOLUTION, AND ANIMAL BEHAVIOR RESEARCH. CATCH UP ON EXCITING NEW PAPERS YOU MAY HAVE MISSED FROM THE JOURNAL, AND MEET SOME TRULY BRILLIANT EARLY CAREER NATURALISTS!

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Credits

Featured Guest: Zegni Triki, Universität Bern, Bern, Switzerland

Host, Editor, Producer: Sarah McPeek, University of Virginia, US

Original Music: Daniel Nondorf, University of Virginia, US

Transcript:

You’re listening to Naturalist Selections, the American Society of Naturalists graduate council’s science podcast featuring graduate student and postdoc-authored research in The American Naturalist.  I’m grad council rep Sarah McPeek and today I’m talking with postdoc first-author Zegni Triki. Zegni is currently starting her own lab at the University of Bern in Switzerland. She formerly completed a postdoc with Dr. Redouan Bshary at the University of Neuchâtel Switzerland, where she conducted fieldwork at the Lizard Island Research Station in the Great Barrier Reef of Australia. Her paper: “Marine Cleaning Mutualism Defies Standard Logic of Supply and Demand” explores the cleaner fish-client fish mutualism on coral reefs as a complex biological market. The cleaner wrasse species Labroides dimidiatus consumes skin parasites of other fish species, reducing their client’s parasite load in the process of feeding. However, cleaner fish don’t always give a 5 star performance. Sometimes, cleaners cheat their clients by eating some of their client’s nutritious skin mucus. Rough biting can cause the client to ‘jolt’ away from the cleaner fish and sometimes, lead them to abandon the interaction altogether. Talk about a ‘yelp’ review! Zegni and her labmates wondered if the density of active cleaners on the reef might contribute to the frequency of cheating behaviors. Perhaps cleaners can charge a ‘higher price’ in the interaction if there are fewer local suppliers of cleaning services. To test this idea, they temporarily removed half the cleaner fish from one part of the reef. One month after the fishes’ removal, they found no change in the quality of remaining cleaner fish’s services. To understand this puzzling result, her lab partnered with two theoretical modelers, Xiang-Yi Li Richter from the University of Stockholm, Sweden and Shun Kurokawa from the University of Tokyo. The resulting model examines how cleaner fish and client fish behaviors play off one another in subtle ways that shift the costs and benefits of cheating, potentially explaining why cleaners on the reef didn’t change their behavior despite the drastic change in market conditions. I talked to Zegni to learn more about this messy, context-dependent mutualism.

Sarah

So the first thing I would love to hear is a little bit more about what it’s like to watch these cleaner wrasses do their work. What do these interactions look like on the reef?

Zegni                                            

You are underwater. We often have like slate and pencil so you can write in the water. Once you are in the water and close to the reef, it’s so easy to find cleaner fish. Often when you see a group of fish together, lots of colors going next to each other, you assume that there is a cleaner fish and often you are right. We try to make videos of half an hour at least so we can get a decent amount of data. So all that you need is really to station yourself somewhere that you are comfortable. You have your camera, you start recording. And just follow these fish. We keep a distance about probably 2 meters from them. Honestly they don’t care whatsoever like coral reef fish, when you are there, especially in this place is research station. They are so used to have researchers around. Our presence, I don’t think it affects their behavior in any way.

Sarah                                                                    

That sounds like such fun field work.

Zegni

It’s really fun. After a while it’s like, really like you are in meditation, all this fish swimming and water and you are just floating with the waves.

Sarah

That’s beautiful. How many interactions do you observe in the course of watching one fish for half an hour?

Zegni

They clean almost nonstop and when they stop it’s often they are checking probably that they might find the better spot. I would say probably more than 80% of their time is really spent in cleaning and interacting with clients fish. So in the span of half an hour I mean we can easily have few hundred interactions that we record. And often we have the male female interactions because they live in a harem and you have a group of probably six to eight female cleaner fish and there’s only one male. And this male cleans a little bit but often checks on his females that they are doing good job, not cheating, they are behaving well. And the females, they adjust to that. So if they’re alone they behave in a way and if the male is around they change their behavior.

Sarah

Wow. I had no idea that it was mostly females doing the cleaning and the males were monitoring their behavior? That’s fascinating.

Zegni

Yeah. The males also they do clean because of course they eat but on top of that they have like extra responsibilities to make sure. And also they need to spawn with the females so they need to gain energy and then turn and spawn with the different females.

Sarah

Is the hypothesis that the males regulating the females cleaning benefits the male because the better she cleans the more resources she gets for reproduction? I’m trying to think about why they do that.

Zegni

Yeah. There is actually conflict because this is a sex changing species, so they all start their lives as females and when they reach a critical body size they change sex to become males. So the male actually tries sometimes to make sure that females are not getting bigger because if the female becomes larger than the usual male or male that is in the group then this female will change sex to become a male and she might actually kick the former male out of the group. Or probably they might fight. So one of the interest the male makes sure is that the females are not getting bigger than him.

Sarah

I see. So it’s more about maintaining dominance, perhaps by limiting how much they’re cleaning. Wow. This is such a cool and complicated system.

Zegni

Oh, it’s very complicated. Like sometimes I spend hours just thinking.

Sarah

So what was your inspiration for doing this big density manipulation on the Reef?

Zegni

So the starting point was a study by a colleague when she did her PhD. And they were just looking to the behavior or the performance of the cleaner fish in the laboratory, in the biological market test that it’s an adaptation to what is going on. And then suddenly they got, like, very distinctive individual differences. Like, they had a group of cleaners, but they were really good and group of cleaner fish that they were, like, really bad. At the time they start pursuing what is going on. And one of the things that came up is that maybe it’s because the cleaner fish densities on these reefs that they were studying. It was so different. Some reefs, they were, like, super rich in the numbers of cleaners and some reefs, they were, like, quite poor. And so it was really based on that logic. We know that this fish species has what is called pelagic larvae form. So when they spawn in the open water, then the larva is free and then it just swims, like probably hundreds of kilometers and then settle on different reefs.And we thought that since they’re coming from different places, it must be the conditions on the reef that are driving the differences. And that’s why we decided to manipulate the reef to see if we can replicate, more or less the findings or additional evidence that they found.

Sarah

Yeah, I think it’s such a clever experiment. Was it challenging to get permission to take half of the fish away from the Reef?

Zegni

Of course, this is Australia, on top of just getting the usual ethics, but Australia has when it comes to ethics, so they’re extremely strict. What we did when we reduced the density, actually, we housed these cleaner fish in the lab in individual aquaria, so they don’t fight. We provide them with food, we made sure that they’re like, we mark them from where we got them and then when we finished the project, we took them one by one and we put them back on the reef.

Sarah

I see. Yeah. I was very relieved to hear that you were able to put the fish back!

Zegni

This research station has lots of facilities there, and it uses running water, but they pump directly from the ocean. So whatever they have and whatever composition of the water, the temperature, everything is exactly the same in the lab.

Sarah

Yeah. Oh, that sounds like fish paradise.

Zegni

And cleaner fish, this is one of the species where they’re quite relaxed in the lab, actually can stay for months. And they are super resilient, like they don’t get sick or anything.

Sarah

Awesome.

Zegni

Yeah.

Sarah

So you left this experiment treatment for about a month. Were you surprised when you went back out there and took all the behavioral data again, that you weren’t seeing a lot of differences between these treatments?

Zegni

Yeah, exactly. I think in science or in academia, it’s always easy to interpret positive findings, but it’s a nightmare to interpret when you don’t find strong effects or no differences. Because does this mean that we truly accept our null hypothesis, that our experiment didn’t affect this, or because it was something in the methods? Maybe we should have waited longer. Maybe we should have taken more than 50%. Maybe we should have gone 80% to get more extreme. So you start putting all these ifs, you know. I think it’s just the classic when you have negative effects that you need to criticize your methods. And also trying to find a potential interpretation.

Sarah

Is that when you turned to collaborating on the modeling work to try and understand what could have happened?

Zegni

Absolutely. So the initial plan. We didn’t have the model at all as part of the project. It was only after we looked at the data and then we had the feeling that probably we need the model just to understand what is going on. And then it made the story more compelling and more complete.

Sarah

So do you think that the results that you saw in the model where basically there’s a lot more nuance to how these interactions shift based on the costs and benefits of interactions, right, there’s a lot of moving parts going on. Is that the way that you now think about these interactions and why you think you didn’t see the results that you did?

Zegni

Absolutely. I mean, the model sort of like proved that everything is possible with the system and depending on the conditions, there’s been a huge shift in the behavior, the way how they foraged, the way, how they interact. And we knew a little bit about this probably before, but combining the model and empirical data proves that it really, it depends. That’s exactly what I think. That was like the take home message. It depends, of course.

Sarah

One thing that I thought about when I was reading the paper is that it seems like the model that you guys used was essentially treating all of the patches as being approximately the same, and it was the cleaner fish themselves who were modulating their behavior. Because these cleaner fish are interacting with so many different fish species, could there be variation among those species in how clients would respond to cleaner fish behaviors and the quality of their services?

Zegni

Actually, that’s a really good question, and I totally agree. I mean, when you do the modeling, there you can simplify to the maximum so you vary only the variable of interest that you want to see how it can affect the outcome. So it’s easier to understand the output. I think when we started for this one, we really wanted to keep it simple, especially that the experiment only manipulated only the cleaner fish. We didn’t manipulate the clients at all. It’s not in this paper but my friend and colleague, he is a modeler and that’s exactly what sort of he’s working on next and he literally tried to add all this complexity about the client species and add things that affect the cleaner decision making like the shape, the color, the quality of the mucus. Probably also the abundance of the parasite and then also the behavior of the client themselves. So that is in the making.

Sarah

Are there fish species on the reef that you know are more amenable to cheating versus not?

Zegni

Yes, cleaner fish definitely have some preferences and there are some studies that they look for the quality of the mucus and they found like actually they go together. The amount of cheating goes positively with the quality of the mucus on these clients.

Sarah

So who has the best mucus on the Reef? What do they like?

Zegni

Mm, that’s a good question. I think maybe parrot fish they have mucus just dripping everywhere. I think maybe also because they make this mucus bag to sleep in, so I think that makes them one of the delicious probably clients because probably they still have some leftover or something from the sac but they always have extra mucus when you look at them.

Sarah

Do you think that parrot fish might suffer lower costs if the cleaner wrasses are cheating and taking their mucus because they have so much of it?

Zegni

Um,  I don’t think that we looked at exactly that trade if it’s more costly for some clients compared to others. So the way we score cheating is that you have a client, you have a cleaner fish is attracting and suddenly you see the client jolting and you assume that this is a pain reaction and it’s because it has been some cheating. It was bit. So we don’t know if when the cleaner fish maybe eats some mucus that the client doesn’t care about, there would be no body jolt. So we never record this because we don’t know if we use more technology in the future and maybe like more advanced cameras that you can see exactly what is happening on the screen surface that we might find out. But for the moment, we don’t really.

Sarah

Yeah. You’re just approximating how choosy they are about cheating by whether they jump backwards when the fish bite them.

Zegni

Yes.

Sarah

I do want to talk about one other thing. That is often an assumption in models and in these theories of how animals should respond to resource levels in their environment. And that’s really the idea that optimal foragers in theory are kind of omniscient. Right. Like they can sense everything that’s around them and they know exactly what the costs and benefits are. And there are definitely evolved preferences and evolved perceptions that they have.  I guess I’ve always been skeptical that they could immediately sense how conditions change and adjust their behavior accordingly. I’m curious if you have thoughts on whether the fish are doing that or whether that might contribute to them not changing their behavior when you all of a sudden lose a bunch of the cleaners.

Zegni

Yeah. So the data that we have from another paper and it’s also linked or can relate to this one, is that the cleaner fish can assemble sort of like information about their environment, but not directly. It’s not the cleaner fish that is hopping from one place to another to check what is going on. But actually they give the information indirectly through their clients. So what we found is that the choosiness level of the client is informing the cleaner fish if there are other neighboring cleaner or other cleaners. If you have, for instance, a client fish, let’s say parrot fish, that its often fussy. So if it’s not happy about the service, it would just swim to the neighbor cleaner and then get a better service from this cleaner fish. Now let’s say that was the case every day for our cleaner fish that we are looking at. And then suddenly this parrot fish, now, even though it’s now receiving really bad service, but it’s not going anywhere, it’s sticking with this cleaner fish. So we found that this cleaner fish will adjust to this change and can even give worse cleaning services because now it becomes aware that this client doesn’t have a choice, cannot go anywhere else. That means the competition is down. So that’s how they get information about their environment and about the competition level in the market. And if the clients, they become more and more choosy and like they’re not satisfied and that means the competition is higher and that gives information to the cleaners. Like be aware. But that’s all that matters when it comes to foraging is really how they adjust to the behavior of their clients because that’s their foot touch and that’s all that they need to do.

Sarah

It’s such a fascinating system because the patches move and the foragers don’t move and the patches are really the ones that are assessing the quality of the environment and giving those cues back to the forager. Interesting.

Zegni

Yeah. It’s like the other way around.

Sarah

But I think it gives us some really interesting insights about different ways that these optimal foraging interactions could play out when you kind of totally reverse roles.

Zegni

Yes, absolutely. And I think the optional foraging theory doesn’t apply. It’s sure. Like the starting point is about foraging, but now that we adopted to biological market, I think it can also be adapted to other markets, like the grooming market. I think it’s the same. It doesn’t involve any food, but it’s a service and you are reaping the benefits. But you reach also like saturation, like how much grooming do you need to lower your stress or feel better? I mean, you reach Saturation level maximum and maybe now you are wasting your time to be sitting there and receiving the grooming. So you need to just get up and get on with your life and do something else. So I think theory might also fit in there in terms of the biological market or more or less like the way how we use it for the cleaning mutualism biological market.

Sarah

Yeah. I’m very curious about how this work has maybe shifted your perspective on the biological market theory and how it can be useful and how maybe it’s, I don’t know, oversimplifying the complexity of these interactions in some ways.

Zegni

Yes. It’s an eye opener. So first of all, it made us more aware that we are just looking for at the tip of the iceberg and the system is way more complex than we thought. And I think the model also has tried to understand what are the drivers of individual decision making. Classic biological market theory models are often evolutionary so they don’t look to the individual decision making. And I think this is one of the things that I’m thinking more about is really how every individual, they make their informative decision.

Sarah

Yeah. There’s so many moving parts because not only are the individuals plastically adjusting their behavior based on what they’re getting from their clients, but the clients, the foraging patches themselves are also adjusting their behavior.

Zegni

Yeah. I think that’s what makes the cleaning materialism system quite a unique biological market where you have actually both parties, they’re adjusting and they’re adjusting during lifetime. And that’s why we need models that they don’t tackle only evolutionary aspects. In the cleaner fish system, you have the first part as a cleaner fish and the foraging patches as the clients, they are both making decisions and it can happen during lifetime and how they adjust. And that’s why we need more models that they can incorporate mechanisms.

Sarah

Absolutely, and that will involve a lot of really good empirical biology to really understand how they’re informing their decisions and how they’re responding to different conditions.

Zegni

Yes, absolutely.

Sarah

So what is the next piece of this interaction that you really want to tackle in your work? It sounds like there’s a lot of moving pieces going on already, but what are you most excited about?

Zegni

Yeah. So one of the big lines is really to go after the female male story and try to understand what is going on and also how the market is changing when they change sex, because now the cleaner fish or the male now has different roles and he can also become a punisher for the females. And when it comes to modeling with my friend and colleague Andres Kenonas. He built a model where he fed the model our empirical data and to see what’s going on. It looks quite promising when it comes to what information they use to make their decisions about choosing between visitor and residents. One of the other research lines we are looking at. It’s why do they choose a visitor over residence? Because that should be optimal. But sometimes they don’t do the optimal choice. And we’re trying to understand what drives some cleaner fish to make the optimal choice, what drives other cleaner fish not to make the optimal choice? And we even try to look at their brains to look at their cognition. It’s just like trying to have a bigger picture deeper and deeper to understand.

Sarah

You’ve got your work cut out for you for sure?

Zegni

Absolutely. Well, not completely for the moment. I work on Gappies in the lab, but I kept working or I keep working on cleaner fish as a side work. It’s like a hobby. I’m keeping it and I’m really enjoying it. It’s just finding it very difficult to let go after all these years working on the system. And I’m so curious about so many things and what is going on and asking questions and coming up with ideas how to test them. I’m having my own dilemma that I cannot really move on.

Sarah

I can’t move on. I’m ready to go jump in the water in Australia, too.

Zegni

It’s just the system every time you uncover one story then you have probably 1015 other questions to ask after so it’s just like it’s not complete yet.

Sarah

Yeah. It’s such a rich and fascinating and fun system. I really enjoyed the paper for those reasons. I think it was really beautiful work. It was also refreshing to see negative results in a big Journal like AmNat I think it was important that we talk about the complexity of the model helps us to understand why we didn’t see these changes when we did our experiments but it’s still valuable to have that information that essentially yeah, it depends.

Zegni

I think it’s like one of the classic things that this might happen more than you think. It’s just the classic approach to science. In the past it was always to be attracted to what is shiny and what is positive but we often, like shy away from negative findings but yeah, digging deeper I think it’s really helpful to understand what is going on.

Sarah

Absolutely. Congratulations on an awesome paper. I’m going to be deeply following all of the work that you do in the future.

 

Zegni

That’s my pleasure. Thank you so much.